The obvious thing that jumps out at me from the photo is the missing condenser for the voltage regulator (the yellow plug with nothing attached). The voltage regulator constantly signals the alternator to charge, then cut-out as the voltage reaches its peak, then charge again. Each time the regulator "switches" the alternator off a voltage surge occurs as the circuit opens. The condenser is placed at that location to absorb the surge. It will also quiet radio frequency (RF) noise in the audio system caused by the "switching". The newer "solid-state" regulators are a bit more efficient than the older mechanical contact-point models but they still generate a surge upon switching.